The purpose of this project is to study the immune mechanisms involved in sporozoite-induced infections, and to develop protocols for immunization with sporozoite antigens. Studies underway are concerned with development of methods for immunizing monkeys with Plasmodium knowlesi sporozoites, and characterization of the structure, function and immunogenicity of surface determinants of sporozoites. The biology of the latent exo-erythrocytic stages of the malaria parasite, the hypnozoites, being examined using Plasmodium cynomolgi.